WASHINGTON, Aug 6 (Reuters) - The U.S. National

Transportation Safety Board on Tuesday is questioning key

witnesses from Boeing ( BA ), Spirit AeroSystems ( SPR ) and the

Federal Aviation Administration on the mid-air cabin panel

blowout of an Alaska Airlines 737 MAX 9 door plug in

January.

During the start of its two-day investigative hearing, the

board released 3,800 pages of factual reports and interviews

from the ongoing investigation.

The incident badly damaged Boeing's ( BA ) reputation and led to

the MAX 9 being grounded for two weeks, a ban by the FAA on

expanding production, a criminal investigation and the departure

of several key executives. Boeing ( BA ) has vowed to make key quality

improvements.

Boeing's ( BA ) senior vice president for quality, Elizabeth Lund,

and Doug Ackerman, vice president of supplier quality for

Boeing ( BA ), are among those who will testify during the hearings

scheduled to last 20 hours over two days, the NTSB said.

Lund told the NTSB in a July 6 interview that the planemaker

is building far fewer MAXs than it is allowed to produce. In

June, it built in the "low 20s and we are working our way back

up. But at one point I think we were as low as eight."

A flight attendant described a moment of terror when the

door plug blew out. "And then, just all of a sudden, there was

just a really loud bang and lots of whooshing air, like the door

burst open," the flight attendant said. "Masks came down, I saw

the galley curtain get sucked towards the cabin."

Terry George, senior vice president and general manager for

Boeing Program at Spirit AeroSystems ( SPR ), and Scott Grabon,

a senior director for 737 quality at Spirit, which makes the

fuselage for the MAX, will also appear, it added.

Last month Boeing ( BA ) agreed to buy back Spirit AeroSystems ( SPR ),

whose core plants it spun off in 2005, for $4.7 billion in

stock.

The hearing will review issues including 737 manufacturing

and inspections, safety management and quality management

systems, FAA oversight, and issues surrounding the opening and

closing of the door plug.

'TOO HANDS OFF'

Boeing ( BA ) has said no paperwork exists to document the removal

of four key missing bolts. Lund said Boeing ( BA ) has now put a bright

blue and yellow sign on the door plug when it arrives at the

factory that says in big letters: "Do not open" and adds a

redundancy "to ensure that the plug is not inadvertently

opened."

In June, FAA Administrator Mike Whitaker said the agency was

"too hands off" in its oversight of Boeing ( BA ) before January. FAA

employees told the NTSB that Boeing ( BA ) employees did not always

followed required processes.

Jonathan Arnold, Aviation Safety Inspector at the FAA, said

a systemic issue he witnessed at Boeing's ( BA ) factory was employees

not following the instructions.

"That seems to be systemic where they deviate from their

instructions. And typically, tool control is what I see most,"

Arnold said.

Also in June, the NTSB said Boeing ( BA ) violated investigation

rules when Lund provided non-public information to media and

speculated about possible causes.

Last month, Boeing ( BA ) agreed to plead guilty to a criminal

fraud conspiracy charge and pay a fine of at least $243.6

million to resolve a Justice Department investigation into two

737 MAX fatal crashes.